1. Field of the Invention
The invention relates to an information processing apparatus, an information processing method, a learning apparatus, a learning method and a program, particularly, relates to the information processing apparatus, the information processing method, the learning apparatus, the learning method and the program capable of accurately removing noise included in images taken by an imaging sensor.
2. Description of the Related Art
The present inventor has proposed class-classification adaptive processing before (for example, refer to JP-A-2002-218414 (Patent document 1)). The class-classification adaptive processing is signal processing which calculates a linear primary formula of pixel values of plural pixels in a prescribed area of an inputted first image and a prediction coefficient calculated in advance by learning processing using teacher images and student images, and thereby calculating second image signals by the inputted first image.
When the first image is an image including noise and the second image is an image from which noise is removed (reduced), the class-classification adaptive processing functions as noise removal processing. When the first image is a SD (Standard Definition) image and the second image is a HD (High Definition) image which has higher resolution than the SD image, the class-classification adaptive processing functions as resolution conversion processing which converts the low-resolution image to the high-resolution image.
In the class-classification adaptive processing disclosed in Patent document 1, the degree of removing noise (noise removal degree) in the noise removal processing or resolution after the conversion in the resolution conversion processing (horizontal resolution and vertical resolution are designated by a user himself by operating a joy stick and the like, and the above prediction coefficient can be changed according to the designated value.
In related arts, in the noise removal processing using the class-classification adaptive processing, an image (signal) received by a tuner and the like or an image (signal) played back from a recording and playback device is made to be the first image, and weak-electric field noise generated at the time of transmission or compression, or noise due to compression distortion are considered as noise to be removed from the first image.
In images obtained by being taken (picked up) by image sensors such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, there are noise having characteristics (noise characteristics) varying according to luminance or exposure time when taking images.
For example, concerning the relation (characteristic) between the noise amount (level) included in an image taken by the image sensor and exposure time when taking images, the longer the exposure time, the larger the noise amount becomes as shown in FIG. 1, therefore, a S/N ratio which is a ratio between a signal and noise decreases as the exposure becomes long. In addition, the relation between luminance (brightness) when taking images and the S/N ratio, the lower the luminance when taking images, the lower the S/N ratio becomes, as shown in FIG. 2.